The invention relates generally to tissue ablation and more particularly to systems and methods for visualizing ablated tissue.
In order for the heart to beat regularly and pump blood efficiently, special conductive tissues in the heart emit electrical pulses that conduct throughout the heart. As the electrical pulses conduct through the heart, they initiate contractions of the heart muscles (i.e., myocardium) causing the heart muscles to contract in an orderly sequence. Diseased heart tissue may disrupt the normal conduction of the electrical impulses and/or produce abnormal electrical activity in the heart, resulting in cardiac arrhythmia. For example, diseased heart tissue may cause electrical pulses to cycle repeatedly within a local region of the heart, inducing sustained twitching of the heart.
Cardiac arrhythmia is commonly treated using a steerable electrophysiological (xe2x80x9cEPxe2x80x9d) catheter that may be precisely positioned anywhere in the heart. The EP catheter is generally used during two distinct phases of treatment for the arrhythmia. In one phase of treatment, the catheter is used to map the electrical activity of the heart in order to identify and locate the source and/or pathway of the abnormal electrical activity associated with the arrhythmia. This procedure is commonly referred to as xe2x80x9cmappingxe2x80x9d. During the other phase of treatment, the same catheter is used to create an ablation lesion at the site where the diseased heart tissue has been located. This procedure is commonly referred to as xe2x80x9cablationxe2x80x9d.
Ablation procedures using EP catheters are typically performed using radio frequency (xe2x80x9cRFxe2x80x9d) energy. In this regard, an EP catheter has one or more ablation electrode(s) located at its distal end. In order to create an ablation lesion at a targeted site, the EP catheter is steered within the heart to position the ablation electrode(s) at the targeted site. Typically, the ablation electrode(s) are placed in contact with the endocardium (inner heart wall) of the targeted site. The ablation electrode(s) then applies RF energy to the targeted site. The applied RF energy causes resistance heating of the tissue adjacent to the ablation electrode(s), producing an ablation lesion at the targeted site.
Successful treatment of cardiac arrhythmia requires that the ablation lesion have a sufficient extent and depth in the myocardium (heart muscle) to effectively eliminate the source and/or pathway of the abnormal electrical activity associated with the arrhythmia. Therefore, systems and methods for visualizing the extent and/or depth of ablation lesions would be highly desirable.
The present inventions are directed to a method for visualizing an ablation lesion. The inventive method comprises injecting a contrast agent into an artery that feeds blood to live tissue surrounding the ablation lesion, and imaging the ablation lesion and the surrounding live tissue with an imager that is responsive to the contrast agent. By way of non-limiting example, the ablation lesion can be located under the endocardial surface of a heart, in which case, the artery can be a coronary artery that feeds live heart tissue. The contrast agent can comprise echogenic particles, e.g., microbubbles, which are typically small enough (e.g., less than 8 microns) to pass through capillaries, so that the open capillaries in the live tissue allow the contrast agent to perfuse therein, while the closed capillaries in the nonviable tissue of the ablation lesion prevent the contrast agent from perfusing therein. In the case of a contrast agent that comprises echogenic particles, the imager can take the form of an interior or exterior ultrasound imager. It should be emphasized, however, that although the preferred embodiment describes an echogenic-based contrast agent and an ultrasound imaging as its preferred means for imaging the ablation lesion, the present invention should not be so limited, and contemplates any contrast agent that is able to distinguish between live tissue and ablated tissue and any imager that is responsive to the contrast agent. For example, optical, MRI or CT imaging technologies may be used with an appropriate type of contrast enhancing agent.